1. Field of the Invention
The present invention relates in general to a fluid delivery device, and more particularly, to a fluid delivery device that includes a water generating electrochemical/chemical pump for controllably delivering small volumes of fluid with high precision and accuracy.
2. Background Art
In many situations it is necessary, or, at least, desirable to deliver small amounts of fluids and/or chemical agents over a relatively long period of time. Such fluids may include, among others, medicaments, lubricants, fragrant fluids, and chemical agents. A very common, traditional apparatus for the gradual administration of fluid into the human body is an intravenous administration set in which gravity induced hydrostatic infusion dispenses a fluid from a familiarly suspended bottle or bag above the patient.
Other methods for the gradual administration of fluids have been devised to eliminate the need for suspending the fluid above the patient and thereby provide the patient with greater mobility. Mechanical pump dispensers use various types of mechanical pumps to expel the fluid from a reservoir. Charged reservoir dispensers store a fluid under pressure in a flexible reservoir and then selectively expel that fluid by the force of internal reservoir pressure, the rate of release often being regulated by a plurality of complex valve systems. Pressurized gas dispensers use a pressurized gas to expel the fluid. Osmotic dispensers rely on a solute that exhibits an osmotic pressure gradient against water to dispense the fluid.
While the above-identified fluid administration device types or techniques have become available, there remains a continuing desire for improvements therein. When small quantities of fluids are to be administered continuously over a period of many hours, it is desirable to have a fluid dispenser that is highly accurate and reliable, is sufficiently small and lightweight to be portable, and is convenient and easy to use. Gas generating devices have been developed that are both portable and accurate for dispensing small volumes. These gas-generating methods include galvanic cells and electrolytic cells.
In galvanic gas generating cells, hydrogen or oxygen gas is formed at the cathode or anode, respectively, as a result of a reaction between a metal or metal oxide and an aqueous electrolyte. A galvanic cell is by definition an electrochemical cell that requires no externally applied voltage to drive the electrochemical reactions. Typically, the anode and cathode of the galvanic cell are connected through a resistor that regulates the current passed through the cell, and, in turn, directly regulates the production of gas which exerts a force on a diaphragm or pistonxe2x80x94thereby expelling the drug. Joshi et al. have been disclosed a number of delivery systems based on the use of galvanic hydrogen generating cell. Examples of such devices are disclosed in U.S. Pat. Nos. 5,951,538, 5,707,499, and 5,785,688. In the cells disclosed in these patents, a zinc anode react with an alkaline electrolyte producing zinc oxide and water molecules are reduced on porous carbon electrode producing gaseous hydrogen.
U.S. Pat. Nos. 5,242,565 and 5,925,030 disclose a galvanic oxygen-generating cell that is constructed much like a zinc/air button cell battery, where a reducible oxide is reduced at the cathode while hydroxyl ions are formed. Hydroxyl ions oxidize at the anode, releasing oxygen.
In contrast to galvanic cells, an electrolytic cell requires an external DC power source to drive the electrochemical reactions. When voltage is applied to the electrodes, the electrolyte gives off a gas that exerts a force on a diaphragm or pistonxe2x80x94thus expelling the drug. Three types of electrolytic gas generating cells have been proposed for use in drug delivery devices. A first type is based on water electrolysis requiring an operating voltage over 1.23 V. A second type, also known as oxygen and hydrogen gas pumps, require lower DC voltage than the water electrolysis systems. Both of these first and second cell types utilize an ion exchanged polymer membrane. A third type of gas generating electrolytic cell is based on the use of an electrolytically decomposable chemical compound that produces a reduced metal at the cathode, and generates gaseous oxygen by oxidation of water at the anode.
U.S. Pat. No. 5,891,097 discloses an electrochemically driven drug dispenser based on electrolysis of water. In this dispenser, water is contained in an electrochemical cell in which porous metal electrodes are joined to both sides of a solid polymer cation exchange membrane, and both the two electrodes are made to contact with water so as to use oxygen or hydrogen generated from an anode or cathode respectively, upon current conduction. Thus, hydrogen, oxygen, or a gas mixture of hydrogen and oxygen, generated by electrolysis of water when a DC current is made to flow between the electrodes, is used as a pressurization source of the drug dispenser.
Electrochemical oxygen and hydrogen pumps are constructed in a similar way to the above discussed water electrolysis cell and are described in several United States patents, including U.S. Pat. Nos. 5,938,640, 4,902,278, 4,886,514, and 4,522,698. Electrochemically driven fluid dispensers disclosed in these patents have an electrochemical cell in which porous gas diffusion electrodes are joined respectively to the opposite surfaces of an ion exchange membrane containing water functioning as an electrolyte. The electrochemically driven fluid dispenser uses such a phenomenon that when hydrogen is supplied to an anode of the electrochemical cell and a DC current is made to flow between the anode and the cathode, the hydrogen becomes hydrogen ions at the anode. When the produced hydrogen ions reach the cathode through the ion exchange membrane, an electrochemical reaction arises to generate gaseous hydrogen thereat. Since the net effect of these processes is transport of hydrogen from one side of the membrane to the other, this cell is also called hydrogen pump. The hydrogen generated and pressurized at the cathode is used as a driving source for pushing a piston, a diaphragm, or the like.
Alternatively, oxygen may be used in place of hydrogen as a reactant in this type of electrochemical cell, wherein the cell then act as an oxygen pump. Thus, oxygen is reduced on one side of a water-containing electrolytic cell and water is oxidized on the opposite side to generate molecular oxygen, with the molecular oxygen so generated being used as the propellant to force liquid from an adjacent reservoir. A variety of different types of devices have been developed and patented.
Gas generating electrolytic cells based on use of electrolytically decomposable chemical compound which produces a reduced metal at the cathode, and generates gaseous oxygen by water oxidation at the anode are disclosed in U.S. Pat. No. 5,744,014. The cell generally includes a graphite anode, an aqueous electrolyte, and a copper hydroxide cathode. As electrical current passes through a circuit in which the cell is connected, copper is plated out in the cathode, and oxygen is released at the anode. To ensure storage stability, an active cathode material is selected such that the cells require an applied voltage for the electrochemical reactions to proceed. A battery is provided in the circuit to drive the current through the gas-generating cell. The rate of oxygen generated at the anode is directly proportional to the current, and acts as a pressurizing agent to perform the work of expelling a fluid from a bladder or other fluid-containing reservoir which has a movable wall which is acted upon as the gas is generated.
While the above-identified electrochemically driven fluid delivery devices are operable for certain applications, they are not optimal for others. In particular, the above-identified fluid delivery devices are based on gas generation, and are suitable for fluid delivery at rates greater than about 20 microliters per day. However, for delivery of very small drug volumes such as about 100 microliters over an extended period of time, and especially for implantable devices, gas generation is not a suitable method for drug delivery. For this purpose, osmotic pumps are more appropriate.
An osmotic pump involves imbibing water or another driving fluid. The pump consists of three chambers: a salt chamber, a water chamber, and a drug chamber. The salt and water chambers are separated by a semi-permeable membrane. This membrane is permeable to water but impermeable to salt. The drug chamber is separated from the other two by a flexible diaphragm. Water imbibes osmotically into the salt chamber creating hydrostatic pressure which, in turn, exerts a force on the diaphragmxe2x80x94thus expelling the drug. The use of osmotic pumps is typically limited to applications requiring constant drug delivery. In order to vary the medicament flow, it is typically necessary to provide numerous osmotic pumps with differing outputs. These limitations make it inconvenient for the patient to use and control such devices. Osmotic pumps also require charging, (the time required for liquid to diffuse through the semi-permeable membrane and begin dissolving the osmagent at steady state) which delays delivery of the medicament, and further limits their suitability for instantaneous or emergency use.
Accordingly, there has been a need for a drug dispenser that is portable, can be miniaturized and therefore implanted, and is highly accurate in the delivering small volumes of fluid with precision and accuracy, that can be programmed at will to change the release rate.
The present invention is directed to a fluid delivery device, comprising: (a) an electrochemical or chemical pump, wherein the pump is capable of generating water; (b) a pump product chamber, wherein the pump product chamber is capable of retaining water generated from the pump; (c) a displaceable member positioned between the pump product chamber and a reservoir, wherein the displaceable member is controllably displaced upon generation of water from the electrical pump; (d) a reservoir, wherein the reservoir is capable of containing a fluid which is delivered upon displacement of the displaceable member; and (e) a housing for containing the pump, the pump product chamber, the displaceable member, and the reservoir.
In a preferred embodiment of the present invention, the pump comprises a selectively permeable membrane, a wet salt layer, a first electrode, a second electrode, an ion exchange membrane, a DC power source, and an electric resistor. In this embodiment, the pump may further include an activation switch and a support member(s).
In another preferred embodiment of the present invention, the selectively permeable membrane is generally permeable to H2O molecules, but generally impermeable to O2 molecules, the first and second electrodes are porous gas diffusion electrodes, and/or the ion exchange membrane is a Nafion type membrane.
Preferably, the displaceable member is selected from the group consisting of a piston, bladder, diaphragm, plunger, and mixtures thereof.
In yet another aspect of the present invention, the reservoir includes one or more apertures and contains a fluid selected from the group consisting of a medicament, lubricant, fragrant fluid, chemical agent, and mixtures thereof.
The present invention is also directed to a process for delivering a fluid, comprising the steps of: (a) providing a fluid delivery device having an electrochemical or chemical water generating pump; (b) generating water from the water generating pump; thereby expanding a volume of a pump product chamber; (c) generating pressure from the expanded pump product chamber; and (d) displacing a displaceable member, and, in turn, controllably expelling fluid from the fluid delivery device.